This thesis proposed the multi-functional solar assisted air source heat pump (MSA-ASHP) system for improving the energy performance of the traditional solar assisted heat pump technology in cooling-dominated buildings in sub-tropical areas like Hong Kong. Firstly, the detailed mathematical models of the MSA-ASHP system are developed and a comprehensive simulation program of the proposed system is built. A number of cases were simulated, which shows that the MSA-ASHP system can provide a much better system performance than traditional air conditioners and water heaters, especially in the air conditioning and water heating (AC/WH) mode. The simulation model of the MSA-ASHP system was extensively validated by experiments, covering all three operation modes. The investigation results demonstrate that the mathematical model is accurate to within 10% of the experimental data. Based on experimental data, an exergy analysis of the MSA-ASHP system was carried out. It is found that the greatest irreversibility occurs in the solar collector, followed by the evaporator, the compressor, the desuperheater, the condenser and the thermostatic expansion valve. The comparison analysis among the four different domestic hot water heating systems shows that the MSA-ASHP system offers the highest energy and exergy efficiencies. Finally, the annual performance of the MSA-ASHP system was analyzed. The monthly solar fraction ranges between 39.4% and 77.4%. The monthly average system coefficient of performance (COP) value is 3.0 throughout a year. An annual energy saving of 54.9% would be achieved when the MSA-ASHP system is adopted instead of the electric water heater plus a conventional air conditioner. The life cycle saving (LCS) analysis for using the MSA-ASHP system in Hong Kong is also conducted. In summary, the simulation model developed for the MSA-ASHP system can provide a useful and effective tool to investigate system performance in different operating modes. The simulation and experimental results demonstrate that the MSA-ASHP system can overcome the mentioned limitations and problems in subtropical areas. Besides, the system performance is improved significantly. Based on the substantial investigation results, it is feasible and desirable to apply the MSA-ASHP system to the cooling dominated buildings in Hong Kong and other subtropical areas.

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